Returns an instance to the pool. By contract, <code>obj</code>
<strong>must</strong> have been obtained using {@link #borrowObject()} or
a related method as defined in an implementation or sub-interface.
@param obj a {@link #borrowObject borrowed} instance to be returned.
Returns an instance to the pool. By contract, <code>obj</code> <strong>must</strong> have been obtained using {@link #borrowObject()} or a related method as defined in an implementation or sub-interface.
@param obj a {@link #borrowObject borrowed} instance to be returned.